Field of the Invention
The present disclosure relates to a device for measuring the membrane fouling index, and more particularly, to a device for measuring the membrane fouling index which can measure the modified fouling index (MFI) and the silt density index (SDI) at the same time and quantify the degree of membrane fouling caused by various kinds of membrane fouling materials, such as particulate materials, colloids, organic matters, and so on, in a short period of time.
Background Art
Reverse osmosis and filtration are one of the technologies that have recently gained attention in the water treatment field. Especially, processes using reverse osmosis are now coming into widespread use in the field of seawater desalination or sewage recycling.
According to a Global Water Intelligence special report entitled “Water Reuse Markets 2005-2015: A Global Assessment & Forecast”, global water reuse capacity is expected to grow from 2 million tons a day today to 5.4 million tons per day in 2015. Over the same period, global seawater desalination capacity is expected to grow from 3 million tons per day to 6.2 million tons per day. Besides, reverse osmosis and filtration are advanced water treatment technologies which are getting attention in the field of surface water and ground water treatment, industrial wastewater treatment, and zero-discharge recycling.
However, membrane fouling, i.e., filtration membrane fouling, is an obstacle to the commercialization of reverse osmosis and filtration. Membrane fouling refers to a situation in which foreign substances present in water flowing into a filtration membrane are deposited or adsorbed on the surface of the filtration membrane in a way that degrades the water permeability of the filtration membrane.
There are various kinds of foreign substances causing membrane fouling, for instance, suspended particles, colloids, organic matters, microbes, and mineral salts such as calcium salts. It is considerably difficult to predict membrane fouling because of these various foreign substances causing membrane fouling.
In general, the silt density index (SDI) is used to predict membrane fouling occurring in reverse osmosis or filtration. The SDI is a measure of possibility at which membrane fouling will occur. The SDI is a method of measurement where influent water is passed through a 0.45 μm pore size filter with 47 mm diameter at a pressure of 30 psi to measure the degree of fouling caused by suspended solids (SS).
As an example, in case of SDI15, the initial time T0 to infiltrate water of 500 ml is measured, and then the time T1 to infiltrate water of 500 ml is measured again after 15 minutes. The ratio of T0 to T1 is used as a measure of membrane fouling. Alternatively, SDI10 may be used.
The SDI measuring method is currently the most widely used method to predict the propensity of membrane fouling by influent water in reverse osmosis or filtration. Generally, if a value measured through the SDI measuring method, namely, an SDI value is less than 3, it is considered to be acceptable. However, if an SDI value is greater than 5, it indicates that severe fouling will occur.
However, the above-described SDI measuring method is an indirect method of evaluating the membrane fouling potential by suspended particles larger than 0.45 μm. So, the SDI measuring method has a limit in that it cannot evaluate the effects of fine materials, such as colloids or organic matters, smaller than 0.45 μm.
Although modified fouling index (MFI) can be used to compensate for the above-mentioned problem of the SDI, the MFI and the SDI have a limit in measurable membrane foulants because the MFI and the SDI basically use the same filtration membrane.
To overcome the problem, methods such as modified fouling index-ultrafilter (MFI-UF) or modified fouling index-nanofilter (MFI-NF) were proposed. However, these methods have difficulty in predicting effects of various types of foulant mixtures that may occur in a filtration membrane because they also use a single type of membrane.
Therefore, various attempts to measure the degree of membrane fouling by various kinds of membrane foulants have been made. As an example, the present inventor suggested earlier-filed Korean Patent Publication No. 10-2013-0081436 titled ‘Device for measuring pollution index of membrane’ which can quantify the degree of membrane fouling caused by various kinds of membrane foulants by arranging hydrophilic microfilter membranes (MF), hydrophilic ultrafilter membranes (UF) and hydrophilic nanofilter membranes (NF) in series.
Moreover, the present inventor proposed earlier-filed Korean Patent Publication No. 2011-0089710 entitled ‘Device for predicting pollution index of membrane’. In Korean Patent Publication No. 2011-0089710, the device for predicting the pollution index of a membrane can itemize membrane foulants and evaluate the degree of membrane fouling by the membrane foulants by connecting a plurality of filtration membranes with different filtration characteristics in series.
However, such conventional methods have a disadvantage in that it is necessary to measure the membrane fouling index two times or more and the conventional methods cannot rapidly cope with a change in water quality because it takes a long time to measure due to the repeated measurement.